FIG. 1 is a sectional view of an intake port formed in a cylinder head of a conventional internal combustion engine.
An intake port 16 is formed in a cylinder head 15 to communicate with a combustion chamber 17 in order to supply a mixture of fuel and air into the combustion chamber. An intake manifold 18 is coupled to an inlet of the intake port 16. Particularly, in case of a gasoline engine, a fuel injector 19 is installed on an intake manifold side at a juncture of the inlet of the intake port 16 and the intake manifold 18. Fuel injected from the fuel injector is mixed with air passing through the intake manifold 18, and the mixture of fuel and air is supplied into the combustion chamber 17. At this time, if a stream of fuel and air is kept in a laminar flow state, the fuel and air are not mixed uniformly, and thus, the occurrence of incomplete combustion and a knocking in the combustion chamber 17 increases. Therefore, in view of improvement in performance of an internal combustion engine, it is an important task to disturb a gas stream to be supplied into the combustion chamber so as to uniformly mix fuel and air with each other.
To this end, there have been developed a variety of conventional swirling units each of which is inserted into an intake manifold or between an intake manifold and an air cleaner to disturb an air stream, thereby inducing the generation of a vortex or turbulence.
However, since such a conventional swirling unit is disposed in an intake manifold or between an intake manifold and an air cleaner, a vortex or turbulence considerably disappears due to friction in a pipe before air that has passed through the swirling unit reaches a fuel injector or a combustion chamber. Accordingly, fuel cannot be efficiently mixed with air, and a mixture of fuel and air supplied to the combustion chamber cannot be formed into a vortex or turbulence thereof within the combustion chamber.